Outriggers for use with mobile cranes and other similar apparatus are necessary to stabilize the crane during lifting operations. Specifically, the outriggers include jacking cylinders with ground engaging pads mounted on opposed laterally extendable support beams. These beams are extended to position the jacking cylinders outwardly in spaced positions with respect to the vehicle chassis. The jacking cylinders are then extended to bring the pads into engagement with the ground, and raise the vehicle so that the wheel assemblies are lifted from the ground. The full weight of the crane is then supported through the outriggers. Advantageously, the wide spacing of the jacking cylinders and pads serves to provide the required side-to-side stability. Typically, a large mobile crane requires two outrigger units, one attached near the rear of the vehicle frame, the other towards the front. Accordingly, good fore/aft stability is also provided.
As the lifting capacity of the crane is increased, so too is the weight of the crane. Accordingly, the outrigger units must be fabricated for greater strength. This necessitates the utilization of stronger, heavier support beams, elongated frame and reinforcements. As a result, the weight of the outriggers also increases. This increase in outrigger weight, added to the already massive mobile crane weight, presents a well known problem. That is, the largest mobile cranes with outriggers can no longer comply with road weight restrictions in many jurisdictions.
As a result, it has become necessary on these larger cranes to use outriggers that are removable from the vehicle frame. These outrigger units are then transported over-the-road separately, usually on low-boy trailers. Because the front and rear outriggers can weigh up to 20,000 -22,000 lbs., and are generally unwieldy due to their relatively long length, it has proven difficult in the past to efficiently handle them. A key handling concern is the amount of turn-around time required for removal at one working site, and the reattachment at the next working site.
It is already known to construct both the front and rear outrigger units with an elongated box frame that can be securely attached to the vehicle frame and with internal hydraulic cylinders to extend and retract the support beams. Removable lock pins extend through mated apertures in the box and vehicle frames and this provides a significant advancement in the overall handling and attachment process. In fact, cranes with this type of removable outrigger units with removable lock pins have become commonplace in the construction equipment industry in recent years.
Despite the advantage provided by the outrigger units that are securely attached by lock pins, other advances in handling have been slow in coming. The considerable handling drawbacks coincident with the use of these removable outrigger units have had a significant adverse effect on sales of these units. The industry in general has heretofore simply found them to be very difficult to handle; i.e. it is too tedious and time consuming a task to both remove them from, and then reattach them to the vehicle.
Attachment is typically accomplished in three steps. First, using the cable and live mast of the crane or some separate, attendant crane, the outrigger unit is properly positioned with respect to the vehicle frame. This positioning is especially difficult when manipulating the front outrigger that is located under and attached to, the underside of the vehicle. The second step is to manually align apertures in the outrigger and vehicle frame that accommodate the securing lock pins. The large mass and inertia of the outrigger complicates the handling as this alignment takes place. Such a fine adjustment is particularly difficult to make under adverse weather conditions, such as high winds, rain and/or cold temperatures. In the final stages of alignment, the prior art outrigger units simply defy precise positioning. Inevitably the process requires a two or three man crew for manual intervention to push and pull on the unit for an inordinate amount of timer as it swings back and forth suspended by the crane.
Removal is accomplished by first disengaging the lock pins, and then removing the outrigger units from the vehicle frame, which is also difficult. Extracting the front outrigger unit is especially difficult because of its awkward location under the vehicle frame, and in most cases requires the attendant crane, as well as the manual intervention. Of course, the unwieldy nature of this outrigger unit especially exacerbates the handling problems during removal. It is not uncommon for the crew to finally have to drag the outrigger unit out from under the vehicle, especially if a separate, attendant crane is not available, subjecting the unit to possible damage.
A number of prior art assemblies, including those disclosed in U.S. Pat. Nos. 4,454,,952 to McGhie, 3,836,012 to Grider et al. and 4,664,411 to Fix, are representative of past efforts to improve the handling of outriggers during both the removal and reattachment phases. Specifically, it has been suggested to provide rollers or wheels on the outrigger units to allow rolling action to and from the attached position on the vehicle frame. This provides some improvement over having to drag the units. The McGhie '012 and Fix '411 patents disclose the concept of providing rollers that travel in corresponding guide rails on the vehicle frame.
Additionally, these prior art designs provide for the pivot mounting (or removal) of at least one of the jacking cylinders to provide clearance for the passage of the outrigger under the vehicle frame. Specifically, the Grider '012 and Fix '411 patents disclose arrangements wherein the jacking cylinder is pivotally mounted allowing it to be tilted into an angled or horizontal orientation for clearance. In both patents the jacking cylinders are directly mounted by brackets on the main outrigger beam, and in such a manner they must be manually tilted. As a result, this phase again requires at least a two man crew. In the Grider '012 patent, both the outrigger unit and jacking cylinders must be manually handled during the removal process.
Thus, despite the advances shown in these references, removal and attachment of outriggers remains a time consuming and difficult task. Attachment, in particular, presents a need for significant manual intervention. Specifically, the prior art procedure necessitates manually manipulating the outrigger unit to bring lock pin receiving apertures into alignment with corresponding apertures on the vehicle frame. Similarly, the cylinders must be manually manipulated before removal of the outrigger unit is possible. The prior art designs fail to provide any feasible approach to insure proper vertical and horizontal alignment of the attachment apertures, or to power tilt the cylinders. Advancements to accomplish these tasks would greatly simplify the procedure. By substantially eliminating this need for painstaking and time consuming manual intervention, a long felt need in handling of removable outrigger units for mobile cranes would be satisfied.
A particular need for an improved apparatus and related method for handling of outrigger units for mobile crane vehicles is thus identified. An improved approach for providing alignment of the units with respect to the vehicle frame is one of these needs, as is making the units so that they are self-powered for removal. Furthermore, a more self-contained unit allowing increased crane capacity, and other attendant features and advantages, are needed.